Automated phase selection for ecg-gated cardiac axial ct scans

ABSTRACT

Provided are one or more systems and/or techniques for mitigating motion artifacts in a computed tomography image of an anatomical object. Extended scan data is received and includes projections and backprojections acquired for parallel rays emitted by a radiation source at different angular locations within a first range of source angles. The projections and the backprojections are compared to identify differences between the projections and the backprojections at the different angular locations. Movement of the anatomical object during acquisition of the extended scan data at the different angular locations is quantified, and short scan data is identified. The short set includes a subset of the extended scan data acquired at different locations within a second range of source angles where the quantified movement of the anatomical object is less than a movement threshold. The computed tomography image of the anatomical object is reconstructed from the short scan data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/310,714, filed Dec. 17, 2018, pending, and claims the benefit ofnational phase entry under 35 U.S.C. § 371 of International PatentApplication PCT/US2018/014177, filed Jan. 18, 2018, designating theUnited States of America, which claims the benefit under Article 8 ofthe Patent Cooperation Treaty to U.S. Provisional Patent ApplicationSer. No. 62/618,216, filed Jan. 17, 2018, for “Optimal Cardiac Phase inProspectively Gated Axial Cardiac CT Scans,” the disclosure of each ofwhich is hereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

The present application relates to the field of computed tomography (CT)and, more specifically, to image reconstruction systems and methods thatat least partially eliminate motion artifacts from axially-aligned CTscans of a beating heart.

BACKGROUND

To improve temporal resolution in axial cardiac scans, short scans(e.g., half-scans, partial scans, etc.) are often used to obtain enoughimage data to allow a full representation of a segment of the heart tobe reconstructed. Short scans involve taking x-ray measurements about aportion, but less than the entire circumference of the heart about anaxis of rotation. Since short scans require less time to complete thanfull, 360° scans for a given scan speed, there is a greater likelihoodof completing a short scan between heartbeats, a period when the heartis relatively stationary. A cross-sectional tomographic image, or“slice,” of the heart is reconstructed from the data collected as aresult of the x-ray measurements. However, heartrates naturally vary,even while a patient is resting. Because the duration of time betweenheartbeats is not constant, triggering a short scan so the short scancan be completed during a time when the heart is relatively stationaryis difficult.

Modern CT scanners have the capability to capture x-ray data for singleslices that are sixteen (16 cm) centimeters in axial length, whichallows reconstruction of an image of the entire heart from a singleshort scan. But most cardiac CT scans continue to be performed with CTscanners that have a collimation requiring four individual slices, eachfour (4 cm) centimeters in axial length, to be assembled into an imageof the entire heart. A portion of the data for one or more of the slicesmay be acquired during a time when motion of the heart during thecardiac cycle is most pronounced. The use of data acquired during thepronounced motion of the heart results in distortions to the resultingtomographic image referred to as motion artifacts. Motion artifactsappearing in one or more of the slices to be assembled into the image ofthe entire heart diminish the quality of the assembled image.

BRIEF SUMMARY

Aspects of the present application address the above matters, andpossibly others. According to one aspect a method of mitigating motionartifacts in a computed tomography image of an anatomical object isprovided. The method includes receiving, at an image reconstructor,extended scan data comprising projections and backprojections acquiredfor parallel rays emitted by a radiation source at different angularlocations within a first range of source angles. The first range ofsource angles extends greater than 240° about an axis of rotation of theradiation source. The projections and the backprojections are comparedto identify differences between the projections and the backprojectionsat the different angular locations. Based on the identified differencesbetween the projections and the backprojections, movement of theanatomical object during acquisition of the extended scan data at thedifferent angular locations is quantified. Short scan data comprising asubset of the extended scan data acquired at different locations withina second range of source angles where the quantified movement of theanatomical object is less than a movement threshold is identified. Thesecond range of source angles is less than the first range of sourceangles about the axis of rotation. The computed tomography image of theanatomical object is reconstructed from the short scan data.

According to another aspect, a computed tomography system is provided.The computed tomography system includes a radiation source, a detectorarray, and an image reconstructor. The image reconstructor is configuredto receive extended scan data comprising projections and backprojectionsacquired for parallel rays emitted by the radiation source at differentangular locations within a first range of source angles. The first rangeof source angles extends greater than 240° about an axis of rotation ofthe radiation source. The image reconstructor is configured to comparethe projections and the backprojections to identify differences betweenthe projections and the backprojections at the different angularlocations. Based on the identified differences between the projectionsand the backprojections, the image reconstructor quantifies movement ofthe anatomical object during acquisition of the extended scan data atthe different angular locations. The image reconstructor is configuredto identify short scan data comprising a subset of the extended scandata acquired at different locations within a second range of sourceangles where the quantified movement of the anatomical object is lessthan a movement threshold. The second range of source angles is lessthan the first range of source angles about the axis of rotation. Theimage reconstructor is also configured to reconstruct the computedtomography image of the anatomical object from the short scan data.

According to another aspect, a non-transitory computer readable mediumcomprising computer executable instructions that when executed via aprocessing unit cause performance of operations, is provided. Theoperations involve extended scan data comprising projections andbackprojections acquired for parallel rays emitted by a radiation sourceat different angular locations within a first range of source angles.The first range of source angles extends greater than 240° about an axisof rotation of the radiation source. The operations include comparingthe projections and the backprojections to identify differences betweenthe projections and the backprojections at the different angularlocations. Based on the identified differences between the projectionsand the backprojections, movement of the anatomical object duringacquisition of the extended scan data at the different angular locationsis quantified. Short scan data is identified, and includes a subset ofthe extended scan data acquired at different locations within a secondrange of source angles where the quantified movement of the anatomicalobject is less than a movement threshold. The second range of sourceangles is less than the first range of source angles about the axis ofrotation of the radiation source. The computed tomography image of theanatomical object is reconstructed from the short scan data.

Those of ordinary skill in the art may appreciate still other aspects ofthe present application upon reading and understanding the appendeddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The application is illustrated by way of example and not limitation inthe figures of the accompanying drawings, in which like referencesgenerally indicate similar elements and in which:

FIG. 1 illustrates an example environment of a computed tomographyimaging modality.

FIG. 2A is a schematic representation of parallel ray emissions atdifferent angular locations within a range of source angles.

FIG. 2B is a schematic representation the acquisition of extended scandata and an identified range of view angles for short scan data.

FIG. 3A is an illustrative embodiment of a motion map graphicallydepicting movement of a heart captured by scan data using parallel raysat different source angles.

FIG. 3B is an illustrative embodiment of a motion curve graphicallydepicting a relationship between quantified movement of a heart anddifferent start views of short scan data.

FIG. 4 illustrates a flow diagram of an illustrative method formitigating motion artifacts in a computed tomography image.

FIG. 5 is an illustration of an example computer-readable mediumcomprising processor-executable instructions configured to embody one ormore of the provisions set forth herein.

FIG. 6 illustrates an example computing environment wherein one or moreof the provisions set forth herein may be implemented.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are generally used to refer tolike elements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details. In other instances, structures anddevices are illustrated in block diagram form in order to facilitatedescribing the claimed subject matter.

Among other things, one or more systems and/or techniques for mitigatingmotion artifacts in a computed tomography image of an anatomical objectare provided herein. Anatomical objects such as a beating heart, forexample, necessarily move when functioning properly. Movements of theheart during a heartbeat may seem to occur according to a fixedperiodical schedule, but the timing of such movements actually varies.Each scan forming a slice of the heart image involves the collection ofextended scan data during an anticipated phase of a cardiac cycle, withthe x-ray, or other radiation source at different angular locationswithin a first range of source angles. The first range of source anglescan cover one, or less than one full rotation about an axis of rotation.

The first range of source angles is greater than at least a minimum,second range of source angles required for reconstruction of an imagefrom the short scan. Because the scan data is collected over the firstrange of source angles at more angular locations about the axis ofrotation than required to reconstruct the image, acquired scan data at aportion of those angular locations can be omitted from thereconstruction. Thus, the second range of angles corresponding to theshort scan data from which the three-dimensional computed tomographyimage is to be reconstructed can be selected anywhere within the firstrange of source angels to mitigate motion artifacts in the reconstructedimage.

Utilizing computational resources to reconstruct the three-dimensionalimages from the short scan data so a user can manually select the imagewith the least noise is computationally inefficient, and time consuming.Instead, the second range of source angles for the short scan data canbe identified utilizing data in the two-dimensional sinogram space.Identification of the second range of source angles can be performedbefore the computed tomography image is generated. The computedtomography image can then be reconstructed from the short scan dataacquired at the identified second range of source angles. Thethree-dimensional computed tomography image reconstructed based on theshort scan data can optionally be reconstructed exclusively of theextended scan data that was captured at angular locations that areoutside of the second range of source angles.

Accordingly, as provided herein, selection of a subset of extended scandata to be used for reconstruction of a computed tomography image isimproved so that motion artifacts are mitigated. In particular, aprojection and backprojection for parallel rays of radiation emitted ateach of a plurality of angular orientations about an axis of rotationare obtained. The projections and backprojections are compared toidentify differences between each projection and backprojection of x-rayradiation at those different angular locations about an axis ofrotation. The projections and the backprojections constitutetwo-dimensional data acquired using parallel rays of radiation as partof the scan. Based on the identified differences, movement of theanatomical object during acquisition of the extended scan data at thedifferent angular locations is quantified. Short scan data is identifiedas including a subset of the extended scan data acquired at differentlocations within a second range of source angles where the quantifiedmovement of the anatomical object is less than a movement threshold.Identification of the short scan data can optionally occur before thecomputed tomography image is generated based on the extended data set.The computed tomography image of the anatomical object is reconstructedfrom the short scan data. Thus, the presence of motion artifacts in thecomputed tomography image resulting from movement of the anatomicalobject during acquisition of the scan data can be efficiently mitigated.

FIG. 1 is an illustration of an illustrative environment 100 comprisinga computed tomography (CT) system that may be configured to generatecomputed tomography images representative of an anatomical object 102(e.g., patient, organ, muscle, tissue, etc.) or aspect(s) thereof. Sucha system may be employed for mitigating motion artifacts that wouldotherwise appear in the computed tomography images as a result ofmovement of the anatomical object 102 during scanning.

It may be appreciated that while the environment 100 in FIG. 1 describesa CT system configured to generate two-dimensional and/orthree-dimensional images of the anatomical object 102 under examination,other radiation imaging modalities are also contemplated for generatingimages of the anatomical object 102, optionally for diagnosticspurposes. Moreover, the arrangement of components and/or the types ofcomponents included in the environment 100 are merely provided as anexample. By way of example, in some embodiments, a data acquisitioncomponent 122 is comprised within a detector array 106.

In the embodiment of the environment 100 in FIG. 1, an examinationapparatus 108 of the CT system is configured to examine one or moreanatomical objects 102, including an anatomical object prone tomovement, such as the heart 205 shown schematically in FIGS. 2A and 2B.With continued reference to FIG. 1, the examination apparatus 108 cancomprise a rotating gantry 104 and a (stationary) support structure 110(e.g., which may encase and/or surround at least a portion of therotating gantry 104 (e.g., as illustrated with an outer, stationaryring, surrounding an outside edge of an inner, rotating ring)). Duringan examination of the anatomical object 102, the anatomical object 102can be placed on a support article 112, such as a bed or conveyor belt,for example, that is selectively positioned in an examination region 114(e.g., a hollow bore in the rotating gantry 104), and the rotatinggantry 104 can be rotated and/or supported about an axis of rotation115, and about the anatomical object 102 by a rotator 116, such as amotor, drive shaft, chain, roller truck, etc.

The axis of rotation 115 for a cylindrical CT system may be located atthe center of the examination region 114, which is also the isocenter ofthe examination apparatus 108. The isocenter is the space through whichthe central ray of a set of beams of radiation 120 passes, and theanatomical object 102 may be positioned within the examination region114 so the region of interest (the heart in the examples below) iscentered at, or located adjacent to the isocenter. The distance R fromthe radiation source(s) 118 to isocenter is represented in broken linesin FIG. 1.

The rotating gantry 104 may surround a portion of the examination region114 and may comprise one or more radiation sources 118 (e.g., anionizing x-ray source, gamma radiation source, etc.) and a detectorarray 106 that is mounted on a substantially diametrically opposite sideof the rotating gantry 104 relative to the radiation source(s) 118. Therotating gantry 104 can be rotated to sweep the radiation source(s) 118through the plurality of angular locations about the axis of rotation115, making full 360° revolutions. The angle β in FIG. 1 generallyrepresents the gantry angle or the source angle at the different angularlocations of the views as described below. During an examination of theanatomical object 102, the radiation source(s) 118 emits fan, cone,wedge, parallel beam (shown in the drawings), and/or other shapedradiation 120 configurations from a focal spot(s) of the radiationsource(s) 118 (e.g., a region within the radiation source(s) 118 fromwhich radiation 120 emanates) into the examination region 114. It may beappreciated that such radiation 120 may be emitted substantiallycontinuously and/or may be emitted intermittently (e.g., a brief pulseof radiation is emitted followed by a resting period during which theradiation source(s) 118 is not activated).

As the emitted radiation 120 traverses the anatomical object 102, theradiation 120 may be attenuated differently by different aspects of theanatomical object 102. Because different aspects attenuate differentpercentages of the radiation 120, an image(s) may be generated basedupon the attenuation, or variations in the number of photons that aredetected by the detector array 106. For example, more dense aspects ofthe anatomical object 102, such as a bone, a metal plate, electroniccomponents, etc., may attenuate more of the radiation 120 (e.g., causingfewer photons to strike the detector array 106) than less dense aspects,such as skin or clothing.

The detector array 106 is configured to directly convert (e.g., usingamorphous selenium and/or other direct conversion materials) and/orindirectly convert (e.g., using photo-detectors and/or other indirectconversion materials) detected radiation into signals that can betransmitted from the detector array 106 to the data acquisitioncomponent 122 configured to compile signals that were transmitted withina predetermined time interval, or measurement interval, using varioustechniques (e.g., integration, photon counting, etc.). It may beappreciated that such a measurement interval may be referred to as a“view” and generally reflects signals generated from radiation 120 thatwas emitted while the radiation source(s) 118 was at a particularangular location relative to the anatomical object 102. Based upon thecompiled signals, the data acquisition component 122 can generateprojection data indicative of the compiled signals, for example.

The detector array 106 may be divided into a plurality of detector cells117 arranged in rows and columns. Using the XYZ coordinates of FIG. 1 asa reference, the detector cells may be arranged in rows that extend inthe X direction, and columns that extend in the Z direction, which is adirection parallel with the axis of rotation 115. The fan angles γ inFIG. 1 are the individual angle of each detector cell 117, as seen fromthe radiation source(s) 118, or the angle relative to the center rayemitted by the radiation source(s) 118. As discussed in detail below,midplane projection and backprojection data may be collected and used tocompare the projections with the backprojections. Midplane data includesonly projection and backprojection data acquired by a centrally locatedportion of the rows of the detector array 106.

For example, an embodiment of the CT system using forty (40 mm)millimeter (or four (4 cm) centimeter) collimation includes sixty four(64) rows of detector cells to capture each of four slices that are tobe assembled into a single three-dimensional image encompassing theentire heart 205. A set of parallel x-ray beams, referred to herein asparallel rays of radiation 120, shown in FIGS. 1 and 2A, emitted by theradiation source(s) 118 encounter the anatomical object 102 before beingreceived by the detector array 106. The midplane data comprisesprojection and backprojection data collected by one, or a plurality ofcentrally-located rows which, in the present example of sixty four (64)rows (numbered sequentially), includes the 32^(nd) and 33^(rd) rows. Thecentrally-located rows are used to collect the midplane data forcomparing the projections and backprojections because the projectionsand backprojections of the centrally-located rows are substantiallyaligned with each other. For a stationary anatomical object 102, thereis little to no offset between the projections and correspondingbackprojections caused by the position of the midplane detector cellsrelative to the radiation source(s) 118, referred to as the cone angle,for example. Thus, any differences or mismatches between the projectionsand backprojections detected by the detector cells in thecentrally-located rows is attributed to movement of the anatomicalobject 102 during acquisition of the projection and backprojection data.

The illustrative example of the environment 100 further comprises animage reconstructor 124 configured to receive the projection andbackprojection data that is output by the data acquisition component122. The image reconstructor 124 is configured to generatethree-dimensional image data (also referred to as three-dimensionalimage(s)) of the anatomical object 102 from the projection data using asuitable analytical, iterative, and/or other reconstruction technique(e.g., back projection reconstruction, tomosynthesis reconstruction,iterative reconstruction, etc.). In this way, the data is converted fromthe two-dimensional projection, or sinogram space to a three-dimensionalimage space of the computed tomography images, a domain that may be moreunderstandable by a user 134 viewing the image(s), for example.

The illustrative environment 100 further comprises a terminal 130, orworkstation (e.g., a computer), that may be configured to receive theimage data (e.g., output by the image reconstructor 124). The terminal130 may also be configured to present the image data and/or informationfor display on a monitor 132 to the user 134 (e.g., medical personnel,etc.). In this way, the user 134 can inspect the image(s) to identifyareas of interest within the anatomical object 102, possibly fordiagnostic purposes. The terminal 130 can also be configured to receiveuser input, which can direct operations of the examination apparatus 108(e.g., a speed of a conveyor belt), for example.

In the illustrated embodiment environment 100, a controller 136 isoperably coupled to the terminal 130. In one example, the controller 136is configured to receive input from the terminal 130, such as user inputfor example, and to generate instructions for the examination apparatus108 indicative of operations to be performed. For example, the user 134may desire to reexamine the anatomical object 102, and the controller136 may issue a command instructing the support article 112 to reversedirection (e.g., bringing the anatomical object 102 back into anexamination region 114 of the examination apparatus 108).

It may be appreciated that the component diagram of FIG. 1 is merelyintended to illustrate one embodiment of one type of imaging modalityand is not intended to be interpreted in a limiting manner. For example,the functions of one or more components described herein may beseparated into a plurality of components and/or the functions of two ormore components described herein may be consolidated into merely asingle component. Moreover, the imaging modality may comprise additionalcomponents configured to perform additional features, functions, etc.,and/or some components described herein may be optional.

Extended scan data is acquired over a first range of source angles thatcan extend greater than 240° about the axis of rotation 115, such as atleast 270° about the axis of rotation 115, or a full 360° about the axisof rotation 115, for example. Short scan data to be used to reconstructthe computed tomography image is identified by the image reconstructor124 to include a subset, but less than all of the extended scan data.For example, the short scan data includes a portion of the extended scandata that is acquired with the radiation source(s) 118 at variousangular locations within a second range of source angles. The secondrange of source angles constitutes a continuous block of, but less thanall of the first range of source angles about the axis of rotation 115.For example, the second range of source angles can be chosen to includeany block of at least 200°, at least 205°, at least 210°, at least 215°,at least 220°, at least 225°, at least 230°, or at least 240° of thefirst range of source angles corresponding to the extended scan data.The second range of source angles corresponds to the short scan dataincluding the projection and backprojection data acquired with theradiation source(s) 118 at locations where the movement of the heart 205is less than a movement threshold, described below (e.g., while theheart 205 is relatively stationary). For example, the heart 205 isrelatively stationary during the diastole or mid-diastole period asopposed to during the QRS complex of the cardiac cycle.

For the sake of clarity and brevity, specific examples of a system andmethod for reconstructing a computed tomography image are describedbelow. However, it is to be understood that the present disclosure isnot limited to the specific numerical values utilized in the examples.Instead, the general concepts described herein are equally applicablefor use with different operational parameters.

In the examples below, the anatomical object 102 is a beating heart 205,and the modality is a CT scanner that acquires projection andbackprojection data based on parallel x-ray radiation emitted by theradiation source(s) 118 at various different angular locations about theaxis of rotation 115. The first range of source angles extends a full360° about the axis of rotation 115 and the second range of sourceangles includes a portion of the first range of source angles thatextends 225° about the axis of rotation 115. The extended scan data willinclude projection and backprojection data acquired at nine hundredsixty (960) views of the heart 205 over the full (e.g., 360°) rotationabout the axis of rotation 115. Thus, for each half of a full 360° scanabout the axis of rotation 115, there are four hundred eighty (480)views. A computed tomography image is to be reconstructed from the dataacquired from six hundred (600) of nine hundred (900) views,corresponding to the 225° second range of source angles. Again, thesenumerical values are merely illustrative, and not meant to beexhaustive.

FIGS. 2A and 2B illustrate operation of the CT system to identify therange of source angles corresponding to short scan data to mitigatemotion artifacts appearing in a computed tomography image of the heart205. The motion artifacts mitigated may be the result of movement of theheart 205 that occurred during acquisition of a portion of theprojection and backprojection data with the radiation source(s) 118 atsource angles included in the extended scan data. The second range ofsource angles is to be identified to exclude at least a portion of theextended scan data that was acquired with the radiation source(s) 118located at those source angles when the movement of the heart 205occurred.

FIG. 2A is a schematic representation of the emission of parallel raysof radiation 120 at different angular locations within a range of sourceangles. The range of source angles over which the scan data is collectedextends between R1 and R2, which is 225° about the axis of rotation 115in FIG. 2A. A 225° range of source angles is sufficient to cause the setof parallel rays of radiation 120 emitted by the radiation source 118 tocapture projection and backprojection data for the depth of the heart205 along the center view 215, which is taken at the center angle β ofthe range R1-R2. Because parallel rays of radiation 120 are generallylinear and orthogonal to the radiation source(s) 118 and the detectorarray 106, the relative alignment of the projections and backprojectionsfor a stationary heart 205 at complementary angles should match (e.g.,the data acquired at 90° and at 270° should match). Any differences ormismatches between the projections and backprojections is attributed tomovement of the heart 205 during acquisition of the projection andbackprojection data.

FIG. 2B is a schematic representation the acquisition of extended scandata and an identified range of view angles for short scan data of thespecific example outlined above. As shown, the extended scan data wascollected for a full scan, over a first range of source angles extending360° about the axis of rotation 115. The first range of source anglesfor the extended scan data is represented by E1-E2 in FIG. 2B. The 960views of the heart 205 are taken at equal intervals over this firstrange of source angles.

The computed tomography image is to be reconstructed from 600 views inthe present example, which corresponds to a second range of sourceangles of 225° for the short scan data. Thus, the views in 225° of thefull 360° full scan are to be used for reconstruction of the computedtomography image. As a result, the possible locations of the center view210 (indicated by dashed lines) for the second range of source anglesfor the short scan data is between S1-S2. S1 is located 112.5° (225÷2)counterclockwise from the top center (0°) of the first range of sourceangles and S2 is located 112.5° (225÷2) clockwise from the top center(0°) of the first range of source angles. At each limit S1-S2 of thesecond range of source angles, the parallel rays of radiation 120emitted perpendicular to the center view 210 capture projection andbackprojection data for the full depth of the heart along the directionof the center view 210.

To determine the second range of source angles corresponding to shortscan data that will mitigate motion artifacts in the reconstructedcomputed tomography image, the projections and the backprojections arecompared to each other. Differences between the projection and thebackprojection for the parallel rays of radiation 120 at each of theangular locations are indicative of movement of the heart 205 during theacquisition of the projection and the backprojection at the respectiveangular locations. If the projections and the backprojections for a viewmatch, the heart 205 is considered to be stationary at that view.

The motion of the heart 205 is quantified for each view based on theidentified differences between the projections and the backprojectionsfor the view. Quantification of the heart motion is based on thecomparisons of the projections and backprojections. Thus, the heartmotion is being quantified in the two-dimensional sinogram space, beforethe computed tomography image based on the acquired scan data isreconstructed. In other words, the heart motion captured by the extendedscan data can be quantified without necessarily reconstructing thecomputed tomography image. The number of parallel rays p is a freeparameter, and can be set to any desired value. In the present example,200 parallel rays are utilized. For the set of parallel rays at eachview (p, θ=β) for β=0-360° or for β=0-180°, the following can bedetermined, for each parallel ray, according to equations [1]-[3]:

$\begin{matrix}{\gamma = {\arcsin \left( \frac{p}{R} \right)}} & \lbrack 1\rbrack \\{\beta_{c\; 1} = {\theta - \gamma - \frac{\pi}{2}}} & \lbrack 2\rbrack \\{\beta_{C\; 2} = {\theta + \gamma + \frac{\pi}{2}}} & \lbrack 3\rbrack\end{matrix}$

where γ is the fan angle shown in FIG. 1, β is the gantry angle at therespective view as shown in FIG. 1, p is the parallel ray number, θ isthe short scan center angle, and R is a distance separating theradiation source(s) 118 and the isocenter of the CT system, which isalso shown in FIG. 1. This quantifying data can be representedgraphically in a motion map and a motion curve, which are shown in FIG.3A and FIG. 3B, respectively.

To generate the motion map, the difference between the projections andthe backprojections along each of the parallel rays emittedperpendicular to the respective view position is determined according toequation [4]:

MotionMap(θ,p)=(S(β_(C1),−γ)−S(β_(C2),γ))²  [4]

The result is a motion map shown in FIG. 3A. The ordinate of the motionmap is the view numbers associated with the start angles for the firsthalf of the scan. In the present example, 960 views make up the full360° scan about the axis of rotation 115, and 480 views make up half arotation about the axis of rotation 115. However, the relationshipsbetween the projection and the backprojection acquired for each viewduring the first half of the scan is expected to match the projectionand the backprojection acquired for each view during the second half ofthe scan. Thus, the ordinate reflects the views between 0 and 480,representing start angles for one half of the full scan.

The abscissa of the motion map shown in FIG. 3A is the parallel raynumber p. For clarity, only two curves 305, each representingdifferences between the projection and the backprojection along one oftwo different parallel rays, are shown in FIG. 3A. Those curvesrepresent parallel ray numbers 150 and 160. However, as noted above, thepresent example utilizes 200 parallel rays so 200 of the curves 305would appear in a complete motion map.

Each curve 305 in the motion map includes segments having differentappearances. In FIG. 3A, the curves 305 include bold segments 310 andsegments 315 that are barely visible. However, according to otherembodiments, the curves 305 can include segments that are color coded,have different line weight, or can be provided with any other type ofappearance. The variable appearance graphically differentiates betweenviews corresponding to start angles that have different quantifiedlevels of heart movement. Thus, in FIG. 3A, start angles adjacent toview 50 and start angles adjacent to view 335 exhibit lower levels ofquantified movement based on the two parallel ray curves 305 shown.

FIG. 3B is a two-dimensional plot of quantified motion value versusstart views of the second range of source angles for the short scandata. The curve 320 shows relative levels of heart motion capturedwithin the scan data acquired in the second range of source angles, ifthe second rang were to start at various start angles. In FIG. 3B, theordinate represents quantified motion values indicative of the averageheart motion included in the scan data, and the abscissa represents thepossible start views of the second range of source angles for the shortscan data. There are 360 views that can be used as possible startinglocations for the second range of source angles for the present example.Out of 960 total views, the computed tomography image is to bereconstructed from 600 views, leaving the 360 views to choose from.

The curve 320 in FIG. 3B is generated by averaging the quantified motionvalues over all parallel rays at each view, then average over sixty (60)angle positions around the center view as follows:

tempMotion(θ)=Σ_(p) MotionMap(θ,p)  [5]

Motion(θ)=Average(tempMotion(θ),60)  [6]

The resulting curve 320 represents a quantified amount of movement ofthe heart 205 that would appear in the reconstructed computed tomographyimage if the second range of source angles started at the variouspossible views. For the example shown in FIG. 3B, it appears a minimumexists in the curve 320 at the starting view of the bold segments 310.Accordingly, to minimize motion artifacts appearing in the computedtomography image, the short scan data can be selected as the subset ofthe extended scan data that was acquired beginning at the view of thebold segments 310. The short scan data includes the portion of theextended scan data acquired from the view of the bold segments 310 toview 909, which are the 600 views from which the computed tomographyimage is to be reconstructed.

The motion map and motion curve are graphical representations of thequantified movement of the heart as a function of view angles generatedprimarily for the benefit of the user 134 (FIG. 1), and for describingthe present technology. However, embodiments of the present CT systemsand methods can optionally identify the minimum quantified movementvalue through numerical analysis, without generating or displaying themotion map or motion curve in FIGS. 3A and 3B.

The short scan data is identified by comparing the quantified movementof the heart 205 in the two-dimensional scan data acquired at thedifferent angular locations to a movement threshold. In the exampleabove, the movement threshold was the quantified movement of the heart205 at each of the possible views, and the lowest value of thequantified movement was selected. The view corresponding to the minimumquantified movement appearing in the motion curve of FIG. 3B was chosenas the start view, so the movement threshold in this example was thesecond lowest quantified motion value. However, according to otherembodiments, the movement threshold may be a defined maximum value ofquantified motion considered to be acceptable, a value within a definedrelationship of the minimum value of the quantified motion, etc.

With the short scan data identified, the computed tomography image ofthe heart 205 can be reconstructed based, at least in part on the shortscan data. The computed tomography image of the heart 205 can bereconstructed exclusively of a portion of the extended scan data that isnot included in the short scan data. In other words, the computedtomography image can be reconstructed without the portion of theextended scan data acquired from views outside of the second range ofsource angles. According to other embodiments, the computed tomographyimage can be generated based, at least in part on the short scan data,optionally supplemented by a portion of the extended scan data acquiredat views outside the second range of source angles.

FIG. 4 is a flow diagram schematically illustrating a method ofdetecting and mitigating motion artifacts in a computed tomography imageof a heart based on two-dimension data. Extended scan data includingprojections and backprojections acquired for parallel rays emitted by aradiation source at different angular locations within a first range ofsource angles is received at step 402. The first range of source anglesextends greater than 240° about an axis of rotation, and can exceed 270°about the axis of rotation, or be a full scan extending a complete 360°about the axis of rotation.

The projections and the backprojections acquired for each of the angularlocations are compared to identify differences there between at step404. Any such differences for an angular location are indicative ofmovement of the heart 205 during acquisition of the projections and thebackprojections at that angular location.

Based on the differences identified between the projections and thebackprojections, movement of the heart 205 during acquisition of theextended scan data at the different angular locations is quantified atstep 406. Quantifying the movement of the heart 205 can be achievednumerically based on equations [1]-[3] above or utilizing any othermodel. The quantified movement values are indicative of the extent ofany differences or mismatches between the projections and respectivebackprojections of the extended scan data.

The short scan data is identified at step 408. The short scan dataincludes a continuous subset of the extended scan data acquired with theradiation source 118 at different locations within a second range ofsource angles where the quantified movement of the heart 205 is aminimum, near minimum, or at least less than a movement threshold. Thesecond range of source angles is less than the first range of sourceangles about the axis of rotation. For the above example, the firstrange of source angles is 360° about the axis of rotation 115, and thesecond range of the source angles is 225° about the axis of rotation115, within the 360° of the first range of source angles.

The computed tomography image of the heart 205 is reconstructed from theshort scan data at step 410. Reconstruction of the computed tomographyimage can be based, at least in part, on the short scan data. Thecomputed tomography image may be reconstructed exclusively of theextended scan data that is not included in the short scan data.According to other embodiments, the computed tomography image can bereconstructed from a combination of the short scan data with a portionof the extended scan data acquired at view angles outside the secondrange of source angles.

Still another embodiment involves a computer-readable medium comprisingprocessor-executable instructions configured to implement one or more ofthe techniques presented herein. An example computer-readable mediumthat may be devised in these ways is illustrated in FIG. 5, wherein theimplementation of embodiment 500 comprises a computer-readable medium502 (e.g., a CD-R, DVD-R, or a platter of a hard disk drive), on whichis encoded computer-readable data 504. This computer-readable data 504in turn comprises a set of processor-executable instructions 506configured to operate according to one or more of the principles setforth herein. In one such embodiment 500, the processor-executableinstructions 506 may be configured to perform a method 508, such as atleast some of the method depicted in FIG. 4. In another such embodiment,the processor-executable instructions 506 may be configured to implementa system, such as at least some of the example environment 100 of FIG.1, for example. Many such computer-readable media may be devised bythose of ordinary skill in the art that are configured to operate inaccordance with one or more of the techniques presented herein.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing at least some of the claims.

As used in this application, the terms “component,” “module,” “system,”“interface,” and/or the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentmay be, but is not limited to being, a process running on a processor, aprocessor, an object, an executable, a thread of execution, a program,and/or a computer. By way of illustration, both an application runningon a controller and the controller can be a component. One or morecomponents may reside within a process and/or thread of execution and acomponent may be localized on one computer and/or distributed betweentwo or more computers.

Furthermore, the claimed subject matter may be implemented as a method,apparatus, or article of manufacture using standard programming and/orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

FIG. 6 and the following discussion provide a brief, general descriptionof a suitable computing environment to implement embodiments of one ormore of the provisions set forth herein. The operating environment ofFIG. 6 is only one example of a suitable operating environment and isnot intended to suggest any limitation as to the scope of use orfunctionality of the operating environment. Example computing devicesinclude, but are not limited to, personal computers, server computers,hand-held or laptop devices, mobile devices (such as mobile phones,Personal Digital Assistants (PDAs), media players, and the like),multiprocessor systems, consumer electronics, mini computers, mainframecomputers, distributed computing environments that include any of theabove systems or devices, and the like.

Although not required, embodiments are described in the general contextof “computer readable instructions” being executed by one or morecomputing devices. Computer readable instructions may be distributed viacomputer readable media (discussed below). Computer readableinstructions may be implemented as program modules, such as functions,objects, Application Programming Interfaces (APIs), data structures, andthe like, that perform particular tasks or implement particular abstractdata types. Typically, the functionality of the computer readableinstructions may be combined or distributed as desired in variousenvironments.

FIG. 6 illustrates an example of a system 600 comprising a computingdevice 612 configured to implement one or more embodiments providedherein. In one configuration, computing device 612 includes at least oneprocessor 616 and memory 618. Depending on the exact configuration andtype of computing device, memory 618 may be volatile (such as RAM, forexample), non-volatile (such as ROM, flash memory, etc., for example) orsome combination of the two. This configuration 614 is illustrated inFIG. 6 by dashed line.

In other embodiments, computing device 612 may include additionalfeatures and/or functionality. For example, computing device 612 mayalso include additional storage (e.g., removable and/or non-removable)including, but not limited to, magnetic storage, optical storage, andthe like. Such additional storage is illustrated in FIG. 6 by storage620. In one embodiment, computer readable instructions to implement oneor more embodiments provided herein may be in storage 620. Storage 620may also store other computer readable instructions to implement anoperating system, an application program, and the like. Computerreadable instructions may be loaded in memory 618 for execution byprocessor 616, for example.

The term “computer readable media” as used herein includes computerstorage media. Computer storage media includes volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information such as computer readableinstructions or other data. Memory 618 and storage 620 are examples ofcomputer storage media. Computer storage media includes, but is notlimited to, RAM, ROM, EEPROM, flash memory or other memory technology,CD-ROM, Digital Versatile Disks (DVDs) or other optical storage,magnetic cassettes, magnetic tape, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to storethe desired information and which can be accessed by computing device612. Computer storage media does not, however, include propagatedsignals. Rather, computer storage media excludes propagated signals. Anysuch computer storage media may be part of computing device 612.

Computing device 612 may also include communication connection 626 thatallows computing device 612 to communicate with other devices.Communication connection 626 may include, but is not limited to, amodem, a Network Interface Card (NIC), an integrated network interface,a radio frequency transmitter/receiver, an infrared port, a USBconnection, or other interfaces for connecting computing device 612 toother computing devices. Communication connection 626 may include awired connection or a wireless connection. Communication connection 626may transmit and/or receive communication media.

The term “computer readable media” may include communication media.Communication media typically embodies computer readable instructions orother data in a “modulated data signal” such as a carrier wave or othertransport mechanism and includes any information delivery media. Theterm “modulated data signal” may include a signal that has one or moreof its characteristics set or changed in such a manner as to encodeinformation in the signal.

Computing device 612 may include input device 624 such as keyboard,mouse, pen, voice input device, touch input device, infrared cameras,video input devices, and/or any other input device. Output device 622such as one or more displays, speakers, printers, and/or any otheroutput device may also be included in computing device 612. Input device624 and output device 622 may be connected to computing device 612 via awired connection, wireless connection, or any combination thereof. Inone embodiment, an input device or an output device from anothercomputing device may be used as input device 624 or output device 622for computing device 612.

Components of computing device 612 may be connected by variousinterconnects, such as a bus. Such interconnects may include aPeripheral Component Interconnect (PCI), such as PCI Express, aUniversal Serial Bus (USB), firewire (IEEE 1394), an optical busstructure, and the like. In another embodiment, components of computingdevice 612 may be interconnected by a network. For example, memory 618may be comprised of multiple physical memory units located in differentphysical locations interconnected by a network.

Those skilled in the art will realize that storage devices utilized tostore computer readable instructions may be distributed across anetwork. For example, a computing device 630 accessible via a network628 may store computer readable instructions to implement one or moreembodiments provided herein. Computing device 612 may access computingdevice 630 and download a part or all of the computer readableinstructions for execution. Alternatively, computing device 612 maydownload pieces of the computer readable instructions, as needed, orsome instructions may be executed at computing device 612 and some atcomputing device 630.

Various operations of embodiments are provided herein. In oneembodiment, one or more of the operations described may constitutecomputer readable instructions stored on one or more computer readablemedia, which if executed by a computing device, will cause the computingdevice to perform the operations described. The order in which some orall of the operations are described should not be construed as to implythat these operations are necessarily order dependent. Alternativeordering will be appreciated by one skilled in the art having thebenefit of this description. Further, it will be understood that not alloperations are necessarily present in each embodiment provided herein.Also, it will be understood that not all operations are necessary insome embodiments.

Further, unless specified otherwise, “first,” “second,” and/or the likeare not intended to imply a temporal aspect, a spatial aspect, anordering, etc. Rather, such terms are merely used as identifiers, names,etc., for features, elements, items, etc. For example, a first objectand a second object generally correspond to object A and object B or twodifferent or two identical objects or the same object.

It may be appreciated that “example” and/or “exemplary” are used hereinto mean serving as an example, instance, or illustration. Any aspect,design, etc., described herein as “example” and/or “exemplary” is notnecessarily to be construed as advantageous over other aspects, designs,etc. Rather, use of these terms is intended to present concepts in aconcrete fashion. As used in this application, the term “or” is intendedto mean an inclusive “or” rather than an exclusive “or.” That is, unlessspecified otherwise, or clear from context, “X employs A or B” isintended to mean any of the natural inclusive permutations. That is, ifX employs A; X employs B; or X employs both A and B, then “X employs Aor B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims may generally be construed to mean “one or more” unless specifiedotherwise or clear from context to be directed to a singular form. Also,at least one of A and B or the like generally means A or B or both A andB.

Although the disclosure has been shown and described with respect to oneor more implementations, equivalent alterations and modifications willoccur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated example implementations of thedisclosure. Similarly, illustrated ordering(s) of acts is not meant tobe limiting, such that different orderings comprising the same ofdifferent (e.g., numbers) of acts are intended to fall within the scopeof the instant disclosure. In addition, while a particular feature ofthe disclosure may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular application. Furthermore, tothe extent that the terms “includes,” “having,” “has,” “with,” orvariants thereof are used in either the detailed description or theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.”

What is claimed is:
 1. A method of mitigating motion artifacts in acomputed tomography image of an anatomical object, the methodcomprising: receiving, at an image reconstructor, extended scan datacomprising projections and backprojections acquired for parallel raysemitted by a radiation source at different angular locations within afirst range of source angles, wherein the first range of source anglesextends greater than 240° about an axis of rotation; comparing theprojections and the backprojections to identify differences between theprojections and the backprojections at the different angular locations;based on the identified differences between the projections and thebackprojections, quantifying movement of the anatomical object duringacquisition of the extended scan data at the different angularlocations; identifying short scan data comprising a subset of theextended scan data acquired at different locations within a second rangeof source angles where the quantified movement of the anatomical objectis less than a movement threshold, wherein the second range of sourceangles is less than the first range of source angles about the axis ofrotation; and reconstructing the computed tomography image of theanatomical object from the short scan data.
 2. The method of claim 1,wherein comparing the projections and the backprojections comprisesconducting a comparison of the projections and the backprojections in asinogram domain, before the computed tomography image is reconstructed.3. The method of claim 1, wherein the computed tomography image of theanatomical object is reconstructed exclusive of a portion of theextended scan data that is not included in the short scan data.
 4. Themethod of claim 1, wherein the first range of source angles extends atleast 270° about the axis of rotation.
 5. The method of claim 4, whereinthe first range of source angles extends 360° about the axis ofrotation.
 6. The method of claim 5, wherein the second range of sourceangles extends up to 240° about the axis of rotation.
 7. The method ofclaim 1 comprising: determining the movement threshold based on thequantified movement of the anatomical object during acquisition of theextended scan data at the different angular locations within the firstrange of source angles.
 8. The method of claim 1, wherein the extendedscan data corresponds to a midplane sinogram captured by one or morecentrally-located sensors in a detector array.
 9. A computed tomographysystem, comprising: a radiation source; a detector array; and an imagereconstructor configured to: receive extended scan data comprisingprojections and backprojections acquired for parallel rays emitted bythe radiation source at different angular locations within a first rangeof source angles, wherein the first range of source angles extendsgreater than 240° about an axis of rotation of the radiation source;compare the projections and the backprojections to identify differencesbetween the projections and the backprojections at the different angularlocations; based on the identified differences between the projectionsand the backprojections, quantify movement of an anatomical objectduring acquisition of the extended scan data at the different angularlocations; identify short scan data comprising a subset of the extendedscan data acquired at different locations within a second range ofsource angles where the quantified movement of the anatomical object isless than a movement threshold, wherein the second range of sourceangles is less than the first range of source angles about the axis ofrotation; and reconstruct a computed tomography image of the anatomicalobject from the short scan data.
 10. The computed tomography system ofclaim 9, wherein the image reconstructor is configured to compare theprojections and the backprojections in a sinogram domain, before thecomputed tomography image is reconstructed.
 11. The computed tomographysystem of claim 9, wherein the image reconstructor is configured toreconstruct the computed tomography image of the anatomical objectexclusive of a portion of the extended scan data that is not included inthe short scan data.
 12. The computed tomography system of claim 9,wherein the first range of source angles extends at least 270° about theaxis of rotation.
 13. The computed tomography system of claim 12,wherein the first range of source angles extends 360° about the axis ofrotation.
 14. The computed tomography system of claim 13, wherein thesecond range of source angles extends up to 240° about the axis ofrotation.
 15. The computed tomography system of claim 9 comprising:determining the movement threshold based on the quantified movement ofthe anatomical object during acquisition of the extended scan data atthe different angular locations within the first range of source angles.16. The computed tomography system of claim 9, wherein the extended scandata corresponds to a midplane sinogram captured by one or morecentrally-located sensors in a detector array.
 17. A non-transitorycomputer readable medium comprising computer executable instructionsthat when executed via a processing unit cause performance of operationsinvolving extended scan data comprising projections and backprojectionsacquired for parallel rays emitted by a radiation source at differentangular locations within a first range of source angles, wherein thefirst range of source angles extends greater than 240° about an axis ofrotation, the operations comprising: comparing the projections and thebackprojections to identify differences between the projections and thebackprojections at the different angular locations; based on theidentified differences between the projections and the backprojections,quantifying movement of an anatomical object during acquisition of theextended scan data at the different angular locations; identifying shortscan data comprising a subset of the extended scan data acquired atdifferent locations within a second range of source angles where thequantified movement of the anatomical object is less than a movementthreshold, wherein the second range of source angles is less than thefirst range of source angles about the axis of rotation; andreconstructing a computed tomography image of the anatomical object fromthe short scan data.
 18. The non-transitory computer readable medium ofclaim 17, wherein the projections and the backprojections are comparedin a sinogram domain, before the computed tomography image isreconstructed.
 19. The non-transitory computer readable medium of claim17, wherein the computed tomography image of the anatomical object isreconstructed exclusive of a portion of the extended scan data that isnot included in the short scan data.
 20. The non-transitory computerreadable medium of claim 17, wherein the operations comprise:determining the movement threshold based on the quantified movement ofthe anatomical object during acquisition of the extended scan data atthe different angular locations within the first range of source angles.